This proposal seeks to identify mitochondrial-targeted drug candidates that decrease mitochondrial reactive oxygen species (ROS) production and reduce oxidative stress-induced tissue damage. We recently discovered a family of small cell-permeable aromatic-cationic peptides (SS peptides) that selectively targets mitochondria and possess antioxidant properties. Studies to date have shown that these peptides are very potent in protecting against oxidative stress-induced apoptosis and necrosis in neuronal cell lines, and demonstrated their ability to protect against ischemia-reperfusion injury both ex vivo and in vivo. Preliminary studies further suggest that these peptides can prevent mitochondrial permeability transition via a mechanism that does not involve scavenging of ROS. Most encouragingly, these peptides have excellent pharmacokinetic profiles and have not demonstrated any toxicity to date in animal studies. We are now seeking short-term support to explore the potential of these novel mitoprotective and antioxidant peptides in reducing the deleterious effects of hyperglycemia. The proposed studies will focus on the effects of hyperglycemia and ROS on pancreatic islet cells and endothelial cells. Our Specific Aims are: 1. To investigate the ability of SS-31 to reduce cell death in endothelial cells and mouse pancreatic islets induced by high glucose; 2. To determine the ability of SS-31 to reduce oxidative stress in endothelial cells and mouse pancreatic islets exposed to high glucose; 3. To determine the site and mechanism(s) of action of SS-31. We propose to demonstrate that SS-31: 1) readily penetrates endothelial cells and mouse pancreatic islets; 2) localizes and concentrates in mitochondria; 3) reduces intracellular ROS production induced by high glucose; 4) protects mitochondrial potential in cells exposed to high glucose; and 5) prevents mitochondrial calcium overload in cells exposed to high glucose. The results from these exploratory studies will guide us to the development of preclinical animal studies for evaluating the therapeutic potential of SS- 31 in the treatment of diabetes and for pancreatic islet transplantation.